Separate chemical freeze-outs of strange and non-strange hadrons and problem of residual chemical non-equilibrium of strangeness in relativistic heavy ion collisions

K. A. Bugaev; D. R. Oliinychenko; V. V. Sagun; A. I. Ivanytskyi; J. Cleymans; E. S. Mironchuk; E. G. Nikonov; A. V. Taranenko; G. M. Zinovjev

arXiv · 1610.03269

Separate chemical freeze-outs of strange and non-strange hadrons and problem of residual chemical non-equilibrium of strangeness in relativistic heavy ion collisions

K. A. Bugaev·D. R. Oliinychenko·V. V. Sagun·A. I. Ivanytskyi·J. Cleymans·E. S. Mironchuk·E. G. Nikonov·A. V. Taranenko·G. M. Zinovjev

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Abstract

We present an elaborate version of the hadron resonance gas model with the combined treatment of separate chemical freeze-outs for strange and non-strange hadrons and with an additional $γ_{s}$ factor which accounts for the remaining strange particle non-equilibration. Within suggested approach the parameters of two chemical freeze-outs are connected by the conservation laws of entropy, baryonic charge, third isospin projection and strangeness. The developed model enables us to perform a high-quality fit of the hadron multiplicity ratios measured at AGS, SPS and RHIC with $χ^2/dof \simeq 0.93$. A special attention is paid to a successful description of the Strangeness Horn. The well-known problem of selective suppression of $\bar Λ$ and $\bar Ξ$ hyperons is also discussed. The main result is that for all collision energies the $γ_{s}$ factor is about 1 within the error bars, except for the center of mass collision energy 7.6 GeV at which we find about 20\% enhancement of strangeness. Also we confirm an existence of strong jumps in pressure, temperature and effective number of degrees of freedom at the stage of strange particle chemical freeze-out, when the center of mass collision energy changes from 4.3 to 4.9 GeV. We argue that these irregularities may signal about the quark-hadron phase transition.

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K. A. Bugaev, D. R. Oliinychenko, V. V. Sagun, A. I. Ivanytskyi, J. Cleymans, E. S. Mironchuk, E. G. Nikonov, A. V. Taranenko, G. M. Zinovjev. 2016-10-11. Separate chemical freeze-outs of strange and non-strange hadrons and problem of residual chemical non-equilibrium of strangeness in relativistic heavy ion collisions. https://arxiv.org/abs/1610.03269

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